Patent application title: Vehicular Guidance System Having Compensation for Variations in Ground Elevation

Abstract:

A system and method of guiding a vehicle comprises establishing elevation
data and corresponding location data for a work area. A particular
location of a vehicle within the work area is determined. Roll data and
pitch data are estimated corresponding to the particular location. The
vehicle is guided based upon the estimated roll data and the pitch data
such that the vehicle follows a desired path.

Claims:

1.-10. (canceled)

11. A system of guiding a vehicle, the system comprising:a data storage
device for storing elevation data and corresponding location data for a
work area;a location-determining receiver for determining a particular
location of a vehicle within the work area;a data processor comprising a
roll estimator for estimating a roll data and a pitch estimator for
estimating pitch data corresponding to the particular location, the roll
data associated with a corresponding lateral slope, the pitch data
associated with a corresponding longitudinal slope generally
perpendicular to the lateral slope, wherein each of the roll data and
pitch data are separately estimated using i) a maximum slope of ground
with respect to a reference point for each cell traversed by the vehicle
corresponding to the particular location, and the maximum slope having a
non-zero longitudinal slope component and a non-zero lateral slope
component, and ii) an aspect angle between a direction of the maximum
slope and an axis with which a direction of travel is coincident; anda
steering controller for guiding the vehicle utilizing the estimated roll
data and the pitch data such that the vehicle follows a desired path.

12. The system according to claim 11 wherein the roll data comprises a
roll angle and wherein the pitch data comprises a pitch angle.

13. The system according to claim 11 wherein the work area is divided into
a group of cells, and wherein each cell is associated with a
corresponding elevation and a respective location.

14. The system according to claim 11 wherein the data storage device
further stores respective slope data and aspect data associated with the
location data, the slope data indicating a change in the elevation and
the aspect data indicating the direction of the slope.

15. The system according to claim 11 wherein the desired path comprises a
substantially linear and arc path segment.

16. The system according to claim 11 wherein the data processor generates
a steering compensation signal to compensate for changes in the roll data
and pitch data between a first location and a second location within the
work area to conform to the desired path.

17. The system according to claim 11 wherein the pitch estimator estimates
the pitch data based on one or more of the following: location data,
elevation data, a current position of the vehicle, an expected position
of the vehicle, vehicle speed, vehicle heading, vehicular velocity, and a
path plan.

18. The system according to claim 11 wherein the pitch estimator estimates
the pitch data consistent with the following equation:θ(Pitch
angle)=Θx=(arc sin(sin Θ sin ψ),where ψ is the
aspect, Θ is the slope, Θx is the longitudinal slope.

19. The system according to claim 11 wherein the roll estimator estimates
the roll data based on one of more of the following: location data,
elevation data, a current position of the vehicle, an expected position
of the vehicle, vehicle speed, vehicle heading, vehicular velocity, and a
path plan.

20. The system according to claim 11 wherein the roll estimator estimates
the roll data consistent with the following equation:Φ(Roll
angle)=Θy=arc sin(sin Θ cos Ψ),where Ψ is the
aspect, Θ is the slope, and Θy is the lateral slope.

Description:

FIELD OF THE INVENTION

[0001]This invention relates to a vehicular guidance system having
compensation for variations in ground elevation.

BACKGROUND OF THE INVENTION

[0002]Vehicles refer to agricultural equipment, construction equipment,
tractors, harvesters, combines, and other off-road vehicles. A
location-determining receiver (e.g., Global Positioning System receiver)
is one of the most useful navigation sensors for user-assisted navigation
or autonomous operation of vehicles. However, the location-determining
receiver alone typically does not provide roll and pitch angular data of
the vehicle. In hilly terrain or other work areas that are not generally
flat, the absence of roll and pitch data may contribute to less
navigational control of a vehicle than is desired or necessary to follow
a generally linear path or another path to a target degree of precision.

[0003]To overcome the limitations of the location-determining receiver,
additional sensors, such as fiber-optic gyros and accelerometers, may be
associated with the location-determining receiver to determine roll and
pitch data for the vehicle during its operation. The additional sensors
and data processing for processing the sensed data tends to add
additional cost to the vehicle. Further, the additional sensors are
generally capable of measuring the current posture (e.g., current roll
and pitch) of the vehicle, but not predicting the anticipated posture
(e.g., future roll and pitch) of the vehicle. Because of the time delay
between sensing of the roll and pitch data and acting upon the sensed
data, the additional sensors may not provide a sensible solution for
improved navigational control of a vehicle. Therefore, a need exists for
a vehicular guidance system having compensation for variations in ground
elevation.

SUMMARY OF THE INVENTION

[0004]A system and method of guiding a vehicle comprises establishing
elevation data and corresponding location data for a work area. A
particular location of a vehicle within the work area is determined. At
least one of roll data and pitch data is estimated corresponding to the
particular location based on the established elevation data. The vehicle
is guided based upon the estimated roll data, the estimated pitch data,
or both such that the vehicle follows a desired path.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005]FIG. 1 is a block diagram of vehicular guidance system in accordance
with the invention.

[0006]FIG. 2 is a flow chart of a method for guiding a vehicle.

[0007]FIG. 3 is a diagram that illustrates a roll angle of a vehicle.

[0008]FIG. 4 is a diagram that illustrates a pitch angle of a vehicle.

[0012]In FIG. 1, the vehicle electronic system 10 comprises a
location-determining receiver 12 and a data storage device 18 coupled to
a data processor 20. In turn, the data processor 20 is coupled to a
steering controller 26. The steering controller 26 is associated with a
steering system 27 of the vehicle.

[0013]The location-determining receiver 12 may comprise a Global
Positioning System (GPS) receiver, a Loran receiver, a Loran C receiver
or some other navigational receiver to provide geographic coordinates of
the receiver 12 or the vehicle on which it is mounted.

[0014]The data storage device 18 may store elevation data versus location
data (e.g., a digital elevation model) of a work area. In one embodiment,
the digital elevation model may divide the work area into a matrix of
cells. The cells may be of uniform size and shape, for example. Each cell
may be associated with location data and elevation data 16. The location
data for a cell may be expressed as geographic coordinates or positional
coordinates associated with a central point within the cell or a boundary
of a cell.

[0015]The topography of the work area may be surveyed by the vehicle or
other equipment prior to completing a planned path or a task associated
with the work area. The survey or another technique establishes location
data versus elevation on a per cell basis over the work area. The
location data versus elevation data 16 may be expressed as a digital
elevation model, a database file, a look-up table or another
representation.

[0016]The data processor 20 may comprise a roll estimator 22, a pitch
estimator 24, and a compensator 25. The roll estimator 22 estimates roll
data for the vehicle based on one or more of the following: location
data, elevation data 16, a current position of the vehicle, an expected
position of the vehicle, vehicle speed, vehicle heading, vehicular
velocity, the interaction between vehicle and ground, and a path plan.
The pitch estimator 24 estimates pitch data for the vehicle based on one
or more of the following: location data, elevation data 16, a current
position of the vehicle, an expected position of the vehicle, vehicle
speed, vehicle heading, vehicular velocity, the interaction between
vehicle and ground, and a path plan.

[0017]The compensator 25 compensates for variation in the roll and pitch
data of the vehicle because of local or global changes in the terrain or
topography of the work area. In one embodiment, the compensator 25
accepts raw path data for the vehicle and outputs a compensated path plan
for the vehicle that considers at least one of the current pitch data,
the current roll data, the expected pitch data, and the expected roll
data of the vehicle. The raw path plan represents positions and headings
for the vehicle, assuming generally flat or ideal terrain, whereas the
compensated path plan represents positions and headings of the vehicle
that compensate for actual terrain with hills, undulations or other
variations in slope or elevation of the ground. The compensator 25 sends
the compensated path plan or compensation data (associated therewith) to
the steering controller 26 to steer the vehicle along a desired path or
route. A steering controller 26 controls the steering and the heading of
a vehicle (e.g., the heading along a planned path) via the steering
system 27 based on a path plan and compensation data.

[0018]The steering controller 26 interfaces the vehicle electronics system
10 with the steering system 27. The steering system 27 may comprise a
hydraulic steering system, a hydraulically assisted steering system, an
electrical steering system, a mechanical steering system or a gear-driven
steering system, or the like associated with the vehicle. A
hydraulically-assisted steering system or electrical steering system may
be configured to support a mechanical steering system, a gear-driven
steering system or a rack-and-pinion steering system, for example.
Hydraulic steering systems and hydraulic assisted steering systems may
have electromechanical actuators for actuating valves or otherwise
controlling the hydraulic aspect of the steering system 27. Electrical
steering systems may use electrical motors (directly or indirectly
through linkages) to change the orientation of one or more wheels that
engage the ground. Compensation data or corresponding corrective signals
may be sent to a steering motor driver or another steering controller 26,
for example.

[0019]FIG. 2 represents a flow chart of a method for guiding a vehicle
having enhanced compensation for variations in ground elevation. The
method of FIG. 2 begins in step S100.

[0020]In step S100, elevation data and corresponding location data for a
work area are established. The work area may be divided into a group of
cells of generally uniform size and shape. For example, the work area may
be divided into a matrix of generally rectangular cells. Each cell is
associated with cellular location data and cellular elevation data. For
example, the cellular location data may represent geographic coordinates
that define a cell boundary and the cellular elevation data may represent
the elevation, slope or other attributes of ground.

[0021]Slope data versus location data and/or elevation data versus
location data is sampled over the work area and preferably within each
cell. A digital elevation map may be created based on an aggregate
assembly of the cellular elevation data and corresponding cellular
location data. FIG. 6 and FIG. 7 represent illustrative examples of
digital elevations maps that could potentially be constructed pursuant to
step S100.

[0022]In step S102, a location-determining receiver 12 determines location
data, including a particular location of a vehicle at a corresponding
time within the work area. The particular location may comprise one or
more of the following: (1) a current location of the vehicle, (2) a
planned location of the vehicle, and (3) a path plan interconnecting the
current location and the planned location of the vehicle.

[0023]In step S104, an estimator estimates at least one of roll data and
pitch data based on the determined particular location and the
established elevation data (e.g., digital elevation map). For example,
the roll estimator 22 may estimate roll data for the vehicle associated
with corresponding location data or position data for a path. Similarly,
the pitch estimator 24 may estimate pitch data for the vehicle associated
with corresponding location data or position data. Step S104 may involve
one or more of the following steps: First, the location-data is used to
reference appropriate corresponding established elevation data. Second,
the roll data, pitch data, or both is/are referenced from the established
elevation data.

[0024]The determination of roll data or pitch data from the established
elevation data may be accomplished in accordance with various alternate
equations or formulae. In one example, the following equations are used
to determine pitch and roll angles:

Φ(Roll angle)=Θy=arc sin(sin Θ cos Ψ), and

θ(Pitch angle)=Θx=arc sin(sin Θ sin Ψ),

where Ψ is the aspect, Θ is the slope, Θx is the
longitudinal slope angle, Θy is the lateral slope angle, and
the direction of travel of the vehicle is coincident with the x axis.

sin Θx=sin Θ cos Ψ

sin Θy=sin Θ sin Ψ,

where Ψ is the aspect, Θ is the slope, Θx is the
longitudinal slope angle and Θy is the lateral slope angle,

[0025]The above equations are based on geometry of the vehicle and the
topography of the land. The roll estimator 22 may determine the roll
angle for the cells along a planed path or raw path, whereas the pitch
estimator 24 may determine the pitch angle for the cells along the
planned path or raw path.

[0026]In another example, static force balance equations, dynamic force
equations, or both, may be used to supplement or replace the above
equations for determining pitch and roll angles. The static force balance
equations and the dynamic force balancing equations may consider one or
more of the following variables: vehicle geometry (size), tire geometry,
vehicle weight and load, vehicle wheelbase and spacing, forces acting on
the tires of the vehicle, and velocities and accelerations of the vehicle
and their components.

[0027]In step S106, the compensator 25 provides compensation data based
upon at least one of the following: (1) estimated roll data, (2)
estimated pitch data, (3) planned path of the vehicle, (4) position of
the vehicle, (5) speed of the vehicle, (6) velocity (i.e., speed and
heading) of the vehicle, (7) acceleration or deceleration of the vehicle
such that the vehicle follows a desired path. The estimated roll data,
the estimated pitch data, or both is/are used to generate a compensation
data or another corrective input for a steering controller 26. It is
anticipated that compensation data with any cell may depend upon (a) the
direction on entry and location of entry of the vehicle into the cell,
(b) the direction of exit and location of exit out of a cell, and (c)
vehicular velocity and (d) an overall planned path of the vehicle.

[0028]In step S108, the steering controller 26 controls steering system 27
with the compensation data from the compensator and location data from
the location-determining receiver such that the vehicle tracks a planned
path (e.g., a generally linear path), regardless of hills or other
fluctuations in the elevation of the terrain. The compensation data may
reduce the jitter, sway or other undesired deviation in position in the
actual path of the vehicle from the target path that might otherwise
occur. The compensation data represent a compensation to compensate for
the difference between an actual location-based guidance path and a
target planned path (e.g., a generally linear path).

[0029]FIG. 3 illustrates a rear view of a vehicle 30 having tires 32 that
rest on the laterally sloped ground 48. The roll angle 34 (Φ) is
defined with reference to the center of gravity 40 of the vehicle 30. The
vertex of the roll angle 34 is coextensive with the center of gravity 40
of the vehicle 30. One first side 44 (indicated by dashed lines) of the
roll angle 34 is generally parallel to unsloped or level ground, whereas
the other side (indicated by the y direction arrow) of the roll angle 34
is generally parallel to the lateral slope 46 of sloped ground. The z
axis 42 represents a normal force of the vehicle 30 on the sloped ground
48.

[0030]FIG. 4 illustrates a side view of the vehicle 30 having tires 32
that rest on the longitudinally sloped ground 49. The pitch angle 54
(Ψ) is defined with reference to the center of gravity 40 of the
vehicle 30. The vertex of the pitch angle is coextensive with the center
of gravity 40 of the vehicle 30. One side 39 of the pitch angle is
generally parallel to unsloped or level ground, whereas the other side 52
of the pitch angle is generally parallel to the longitudinal slope of
sloped ground. The z axis 42 represents a normal force of the vehicle 30
on the ground sloped ground 48.

[0031]FIG. 5A illustrates the slope of the terrain of at least a portion
(e.g., a cell) of the work area. The slope Θ comprises a lateral
slope 46 (Θy) and a longitudinal slope 50 (Θx).
FIG. 5A and FIG. 5B illustrate an aspect which represents the direction
of the maximum slope. In one embodiment, each cell may be defined by a
slope (Θ), which comprises the following components: a longitudinal
slope (Θx) and a lateral slope 46 (Θy). The aspect
51 or aspect angle (Ψ) is the direction of the maximum slope,
referenced from the x axis. The aspect angle is the angle between the x
axis and the maximum slope. The direction of travel may be defined
coincident with the x axis. The slope relationship is defined as follows:

sin Θx=sin Θ cos Ψ

sin Θy=sin Θ sin Ψ,

where Ψ is the aspect and Θ is the slope, Θx is the
longitudinal slope, band Θy is the lateral slope 46.

[0032]The roll and the pitch data for each cell or another portion of the
work area may be estimated by the application of the following equations:

Φ(Roll angle)=Θy=arc sin(sin Θ cos Ψ), and

θ(Pitch angle)=Θx=arc sin(sin Θ sin Ψ),

where Ψ is the aspect, Θ is the slope, Θx is the
longitudinal slope angle, and Θy is the lateral slope 46.

[0033]In practice, the above equations may be modified or accompanied by
static force balance equations and dynamic equations with respect to the
vehicle 30 operating in the work area. The static force balance and
dynamic equations may include one or more of the following variables: (a)
vehicular geometry and dimensions, (b) vehicular weight and load, (c)
forces acting on the tires 32, (d) velocities and accelerations, and (e)
other vehicular attributes or specifications.

[0034]FIG. 6 illustrates a first digital elevation model map in graphical
form. It is understood that any digital evaluation model map may be
stored as a table, a database or an inverted file. The digital elevation
model divides a work area into uniform-shaped cells (e.g., rectangles or
squares). A uniform value for elevation and slope may be assumed within
any single cell. The cell size may depend upon the availability of
topographical data for the work area. A cell size that is less than or
equal to the vehicle length is preferable to obtaining a sufficiently
accurate estimate of pitch data and roll data. The first digital
elevation map of FIG. 6 divides the work area into a five by five area of
rectangular cells, wherein each cell has elevation data (E) and location
data (L). For example, the cell identifier of row 1, column 1, is
associated with E1,1, and L1,1; the cell identifier of row 2, column 2 is
associated with E2,2 and L2,2; the cell identifier of row 3, column 3 is
associated with E3,3 and L3,3; the cell identifier of row 4, column 4 is
associated with E4,4, and L4,4; and cell identifier of row 5, column 5 is
associated with E5,5 and L5,5.

[0035]FIG. 7 illustrates a second digital elevation model map in graphical
form. The second digital elevation map of FIG. 7 divides the work area
into a four by six area of generally rectangular cells. Each cell within
the second digital elevation model map may be assigned or associated with
a corresponding uniform elevation data (E), slope data (S), aspect data
(A), and location data (L). For example, the cell identifier of row 1,
column 1, is associated with E1,1, L1,1, S1,1, and A1,1; the cell
identifier of row 2, column 2 is associated with E2,2, L2,2, S2,2, and
A2,2; the cell identifier of row 3, column 3 is associated with E3,3,
L3,3, S3,3, and A3,3; the cell identifier of row 4, column 4 is
associated with E4,4, L4,4, S4,4, and A4,4; the cell identifier of row 1,
column 6 is associated with E1,6, L1,6, S1,6, and A1,6; and the cell
identifier row 4 , column 6 is associated with E4,6, L4,6, S4,6, and
A4,6. FIG. 6 and FIG. 7 are illustrative examples of representations of a
digital elevation model; actual representations may vary in their size,
shape, the number of cells, number of variables per cell, and still fall
within the scope of the claimed invention.

[0036]Having described the preferred embodiment, it will become apparent
that various modifications can be made without departing from the scope
of the invention as defined in the accompanying claims.